Silicon nitride substrate and method of manufacturing the same

Abstract

Color unevenness generated on a surface of a silicon nitride substrate is reduced. A silicon nitride substrate formed by nitriding silicon containing in a sheet-shaped green body includes a first surface and a second surface opposite to the first surface. In this case, when color difference between a center and an edge of at least one surface of the first surface and the second surface is expressed to be “ΔE*ab”, a relation “ΔE*ab≤1.5” is established.

What is claimed is: 
     
       1. A silicon nitride substrate comprising:
 a first surface; and 
 a second surface opposite to the first surface, 
 wherein a planar shape is rectangular, each side length of which is equal to or larger than 100 mm, 
 a thermal conductivity is equal to or higher than 110 W/(m·K), 
 when color difference between a center and an edge of at least one surface of the first surface and the second surface is expressed to be “ΔE*ab”, a relation “0<ΔE*ab≤1.5” is established at all edges positioned inward from each corner by 15 mm in a direction to the center. 
 
     
     
       2. The silicon nitride substrate according to  claim 1 ,
 wherein a relation “0<ΔE*ab≤0.8” is established. 
 
     
     
       3. The silicon nitride substrate according to  claim 1 ,
 wherein lightness at each of the center and the edge is equal to or higher than 70. 
 
     
     
       4. The silicon nitride substrate according to  claim 1 ,
 wherein chromaticness at each of the center and the edge is equal to or higher than 10. 
 
     
     
       5. A method of manufacturing a silicon nitride substrate comprising steps of:
 (a) preparing a slurry containing silicon power; 
 (b) forming a green body from the slurry; and 
 (c) sintering the green body in a furnace, 
 wherein the step (c) includes a nitriding step of nitriding the green body by heating the green body at a predetermined heating temperature, and, 
 in the nitriding step, an average of a temperature rise amount per unit time in a range from 1270° C. to 1340° C. is equal to or lower than 3.1° C./h. 
 
     
     
       6. The silicon nitride substrate according to  claim 2 ,
 wherein lightness at each of the center and the edge is equal to or higher than 70. 
 
     
     
       7. The silicon nitride substrate according to  claim 2 ,
 wherein chromaticness at each of the center and the edge is equal to or higher than 10. 
 
     
     
       8. The silicon nitride substrate according to  claim 3 ,
 wherein chromaticness at each of the center and the edge is equal to or higher than 10.